Thermionic tube



P. F. SCOFIELD THERMIONIC TUBE Jan. -1, 1935.

Filed July 18, 1932 INVENTOR,

HIL/P F. SCOF/ELD. wfw

ATTORNEY Patented Jami, 1935 rnm vnomo TUBE Philip F. Scofield, PaloAlto, Calif., assignor to Heintz & Kaufman, Ltd., San a corporation ofNevada Francisco, Calif.,

Application July 18, 1932, Serial No. 623,115

2 Claims. (01. zan -27.5)

My invention relates to a thermionictube having a variable amplificationfactor, and more, particularly to such a tube inwhich a wide rib-, bonfilament is positioned between a control 'electrode and the anode, the.fiat surface ofthe ribbon being at'right angles to the plane of thecontrol electrode. t r I Amongthe objects of myinvention are: To'pro-'vide a thermionic tube having a variable mu.- factor or amplificationfactor; to'provide a vari-' able mu tube of simple and economicalconstruction; to provide a thermionic tube having a mufactor whichvaries from point to point of the cathode emissive surface; and toprovide avariable mu tube designed for the eliminationofdistortion inradio receiving sets. r I

Other objects of my invention will be apparent or will be specificallypointed out in the description forming a part of this specification, butI do not limit myself to the embodiment of my invention hereindescribed, as various forms may be adopted within the scope of theclaims.

Referring to the drawing: i

Figure 1 is a view, partly in section and partly i. in elevation, of avacuum tube embodying this invention.

, Figure 2 is a cross sectionalview taken in the plane indicated by theline 2-2 in Figure 1.

Figure 3 is a longitudinal section of the elements alone, taken in aplane indicated by the line 3-3 in Figure 2. y

In broad terms my invention comprisesa thermionic tube having an anodeand control electrode, preferably located in parallel planes. A cathodecomprising a wide ribbon filament is 1 positioned between theelectrodes, with one narrow edge close to and parallel to the controlelectrode. The major surface of the ribbon is preferably at right anglesto the plane of the control electrode. In the drawing, which representsa preferred embodiment of my invention, a bulb 1 is proportedrespectively by'the anode supports. '7 and the control electrodesupports 9. One of each of these supports may be a dummy, or a supportwhich does not extend all the way through the pinch. v

The anode and control electrode are preferably a formed as fiat plates,provided with flanges'lo for stiffening purposes, and made of nickel, ortantalum. i It is customary to fasten such plates -to the support wiresbyQelectric welding.

A bridge support 11 extends upwardly from the top of bothanode andcontrol electrode and is inserted into a filament bridge 12 ofinsulating material such as lava or isolantite, which serves ,both tospace and maintain the plates and 6 parallel, and to providea bearinghole 14 through ,which is placed a filament hook 15.

The shank 16 of this hook is inserted into an extension spring 1-7fastened to the shank by the weld 19.

Filament leads '20, both extending through the of ,a lwideinvertedV-shaped ribbon filament 21 i which has its apex 22 caught bythe filament hook so that the entire filament is firmly held in tensionby the spring 17. V

The filament leads are bent and adjusted until one narrow edge of theribbon is close to the control electrode and equally spaced from it. Atthe same time the wide surface is positioned at right angles to theplane of the control electrode.

Afterthese adjustments'have been made the tube is exhausted and. sealedoff the pumps in the usual manner, and provided with a base 24. The leadwires 25 coming from the electrodes are inserted' into base prongs 26 inthe customary order and. secured to the prongs by soldered joints 2'7.

In operation as used in conjunction with the proper circuits to takeadvantage of its variable mu characteristics, the control electrode willhave a high degree of control over the emission from that portion of theribbon closest to the electrode, and a lesser degree of control over theemission from the far portions of the cathode ribbon. The variation ofmu-factor may be increased by increasing the width of the ribbon.

I am. aware of the fact that ribbon filaments have been used in ordinarytubes in edge relation to the electrodes, but in all such cases theribbon has been made very narrow so that uniform control might be had ofall the emission. I deliberately utilize a wide ribbon, and with suchwide ribbons a wide variation in mu-factor may be ;obtained. Theadvantages of a high amplification factor are retained at normalvoltages, while at high biases, the low distortion characteristics .edto three-element tubes, it is obvious that the same general resultsandadvantages will be obtained when used in conjunction with tubeshaving additional control, accelerating or shielding 2. Means forproducing a variable mu factor in electrodes. a thermionic tubecomprising an anode, a control I Olaim! electrode, and a wide ribbonfilament interposed A thermionic tube comprising an anode between saidanode and cathode, one narrow edge control electrode and cathode havingflat of said ribbon being closer to said control elecemissive surfaceinterposed between said anode tmde than the other narrow edge andcontrol electrodes, and having its narrow electrode.

- edge closely adjacent and parallel tothe control I :1 I I r v EPHILIPF SCOFIELD

